Blizzard Entertainment'sreal-time strategy game series StarCraft revolves around interstellar affairs in a distant sector of the galaxy, with three species and multiple factions all vying for supremacy in the sector. The playable species of StarCraft include the Terrans, humans exiled from Earth who excel at adapting to any situation; the Zerg, a race of insectoids obsessed with assimilating other races in pursuit of genetic perfection; and the Protoss, a humanoid species with advanced technology and psionic abilities, attempting to preserve their civilization and strict philosophical way of living from the Zerg. Each of these races has a single campaign in each StarCraft real-time strategy game. In addition to these three, various non-playable races have also been part of the lore of the StarCraft series; the most notable of these is the Xel'Naga, a race which features prominently in the fictional histories of the Protoss and Zerg races.

The original game has sold over 10 million copies internationally, [1] and remains one of the most popular games in the world.[2][3][4] One of the main factors responsible for StarCraft's positive reception is the attention paid to the three unique playable races, for each of which Blizzard developed completely different characteristics, graphics, backstories and styles of gameplay, while keeping them balanced in performance against each other.[5] Previous to this, most real-time strategy games consisted of factions and races with the same basic play styles and units with only superficial differences. The use of unique sides in StarCraft has been credited with popularizing the concept within the real-time strategy genre.[5] Contemporary reviews of the game have mostly praised the attention to the gameplay balance between the species,[6] as well as the fictional stories built up around them.[7]

A Protoss warrior and a Zerg creature, as they appeared during StarCraft's production in 1996.

Across the course of the game's development, the races and graphics of StarCraft have changed drastically from Chris Metzen's original concept art. In particular, since their initial public debut at E3 1996,[8] the Zerg have seen extensive changes to their visual design. This was primarily due to Blizzard's attempt to steer the game away from the visual appearance, unveiled at the 1996 E3, that had earned the game a derisive label of "Warcraft in space".[9] The Zerg were originally known as the "nightmarish invaders", later becoming the "Zurg", and then renamed again to its current spelling to avoid any potential trademark conflicts with Pixar'sToy Story character of Emperor Zurg.[8] In the early alpha versions built by Bob Fitch, the Zerg still showed their insect-inspired base, but their appearance was heavily dominated by spikes and bright shades of blue and purple. Early Protoss concept art showed a green and blue color scheme in their mechanical armor. Closely hewing to the familiar visual style of Warcraft II: Tides of Darkness, the build received much criticism from industry press, prompting a redesign of the game engine and an overhaul of the races' respective visual designs.[9]

This new version, unveiled in early 1997,[9] still used the Warcraft II engine as its base, but with distinct changes. The Terrans and the Protoss were detailed to a much greater extent than at E3 1996, revealing many of the game's units in forms similar to those of the final product. Blizzard Entertainment also began the careful task of balancing the game's three races.[9] However, in February 1997, Bob Fitch declared that, despite these efforts, the game engine was simply incapable of delivering features requested by the developers: cloaking, burrowing and many other special effects.[10] The development team therefore embarked upon a two-month overhaul of the graphics engine. This new beta version was far closer to the release version, as the races took on their now-recognisable graphical styles: the brown insectoid design of the Zerg, the sleek yellow armour of the Protoss, and the grey machinery of the Terrans.[11] Most of the unit designs were established at this point, their graphics only undergoing minor changes. Several game features were also added at this stage in the development that never made it into the final release, such as ships banking as they turned,[12] transport ships landing on the ground to pick up and drop off passengers,[12] and efficiency ranks, although Terran units would retain ranks as a purely aesthestic feature. The Terran Valkyrie-class missile frigate also appeared in this build of the game,[11] although it was removed before the final release, only to be reintroduced later in the Brood War expansion.

The Protoss are a race in the StarCraft series. They are composed of two societies, the conservative Khalai Protoss and the exiled dark templar. The Protoss are depicted as a physically strong species with access to advanced psionic abilities. The Protoss are considered the most technologically advanced race of the series and are the focus of two episodes within StarCraft and its expansion Brood War, as well as featuring in campaigns in the authorized add-ons Insurrection and Retribution. Protoss strategy in-game is usually built around the quality of units the player controls rather than the quantity. Originating from Aiur, a planet on the fringe of the galaxy, the Protoss are normally shown in the games and the novels of the series as the nemesis of the Zerg.

Protoss society is shown in the background of the series to have been tribal with a strong warrior culture, until a planet-wide civil war allowed a mystic, Khas, to access a natural psionic link shared by all Protoss.[13] Khas' discovery and teachings, labelled the Khala, are then used as a base for a new caste-based society. The Judicator caste forms the Conclave, the ruling body of the Khalai Protoss. The Templar caste constitutes the military, and the Khalai caste includes all other Protoss.[14] The player controls a Templar character in the Protoss campaigns of all the video games to date. Khalai Protoss society is depicted as collectivism, being stubbornly conservative while maintaining the warrior culture and honor values of the tribal system.[15]

The backstory presented in StarCraft's manual and in the novel Shadow Hunters also shows the rise of a second society of Protoss known as the Nerazim. They are a sizeable minority of the Protoss who reject the Khala out of fear of losing their individuality inside the psychic link. The Nerazim are treated as heretics by the Khalai Protoss and are forcibly evicted from Aiur.[16] Despite their persecution, the majority of Dark Templar do not hold anything against their estranged brethren, seeking to defend Aiur in any way they can. The Nerazim are presented as nomadic, liberal society, only settling on the planet Shakuras to study a Xel'Naga temple there. During the Brood War event, the Protoss lose their homeworld of Aiur to the Zerg (even with the Overmind being destroyed by Tassadar) and the Khalai Protoss are forced to escape and seek refuge on Shakuras, by then the homeworld of the Nerazim Protoss. After the conclusion of StarCraft, the two groups begin to reconcile, but the reconciliation is marred by mutual distrust.[17]

StarCraft II: Wings of Liberty also depicts a third faction of Protoss, known as the Tal'Darim. Left behind on Aiur during the Zerg invasion, the splinter group lost their connection to the Khalai society and regressed to a state of aggression and fanaticism. During the events of Heart of the Swarm and Legacy of the Void the Tal'Darim society is further explained to worship Amon, a Fallen Xel'Naga who seeks to extinguish all life and recreate the universe in his image. The Tal'Darim follow a hierarchy known as the 'Chain of Ascension' which they believe, the higher up the chain, the closer they come to Amon. Tal'Darim warriors can challenge other Tal'darim in higher ranks to ascend in the chain through a rite called Rak'Shir.

Starcraft II: Legacy of the Void introduces a fourth subfaction of the Protoss race, the Purifiers. The Purifiers are synthetic constructa created by the Protoss which house the preserved spirits of fallen Protoss warriors. The Purifiers rebelled against the Khalai Protoss in 'ancient' times because they weren't viewed as equals, but rather as tools used by the Protoss. The Purifiers were deactivated and sealed away in a large vessel known as the 'Cybros' and brought to a planet known as Endion where they were supposed to be buried.

Both the Tal'Darim and the Purifiers are sought out by Artanis in Legacy of the Void to unite all Protoss factions to fight Amon. The Daelaam are the unified protoss of the Khalai, Nerazim, Tal'darim, and Purifiers; their armed forces are named likewise.

The Protoss are humanoids, with two luminous eyes, typically gold, green, or blue. With two fingers flanked by two opposable thumbs on each hand, two large toes on each foot (four small toes in earlier games), digitigrade legs, broad chests and shoulders with narrow waists, Protoss are very agile and physically strong. A bony crest extends back from the crown of the head, with long neural strands sprouting from the back of the head. These strands facilitate the basic psychic communal link all Protoss naturally share.[18] Each Protoss has a different skin shade that corresponds to the tribe from which they are descended.[19] The Protoss do not possess any visible ears (but they can hear, as when Terrans speak to them or hear what they are thinking), mouths or noses, but are able to communicate telepathically and possess strong olfactory sensitivities. Protoss do not need to eat or drink, but are shown in The Dark Templar Saga to instead absorb energy from a form of photosynthesis.[20] The average life expectancy for a Protoss is about one thousand years. Little is known of the internal anatomy of the Protoss.

In contrast to the other two species, Protoss units and buildings display smooth and elegant designs, usually emphasising gold and blue colors on armor and vehicles/ships and feature blue energy highlights. The dark templar units tend to display silver rather than gold and have green energy highlights. In Starcraft II Protoss are also featured in dark shades with green energy highlights. These Protoss were corrupted by the Hybrids. The Protoss Tal'Darim faction sports black/grey with red colors and also features red energy highlights. Last but not least the Purifiers sport generally white with black accents and feature orange energy highlights. Protoss units are generally more expensive and slower to produce in-game compared to Zerg or Terran units, but are conversely also more powerful and efficient in combat. All Protoss units and buildings are covered by a regenerating energy shield, further increasing the amount of damage that they can endure, although the Protoss previously had no way of healing or repairing their units.[21] By 2505 in the StarCraft timeline, specifically in the Legacy of the Void expansion to StarCraft II, the Protoss develop a new method to restore their energy shields, by using one of their "spellcaster" units, Sentries. [22]

The Protoss are the focus of the third campaign of StarCraft. In the events immediately preceding the beginning of the game, the Khalai Protoss have become aware of a Zerg invasion of Terran worlds, and respond by dispatching a fleet commanded by the high Templar Tassadar to destroy infested Terran worlds. Tassadar instead disregards his orders to massacre the Terran populations, attempting to destroy the Zerg by conventional means. Tassadar later meets a Dark Templar, Zeratul, and embraces the Dark Templar culture, prompting the Khalai Protoss to brand Tassadar as a traitor. Zeratul unwittingly reveals the location of the Protoss homeworld Aiur to the Zerg, leading to a Zerg invasion that devastates the planet. At the end of StarCraft, Tassadar sacrifices himself to save his people and their Terran allies by destroying the Zerg Overmind[23] by crashing his carrier, the "Gantrithor", directly into the hivemind.

The Protoss return in Episode IV of Brood War, the expansion to StarCraft. Following immediately on from the conclusion of StarCraft, Zeratul and a ranking templar Artanis evacuate the surviving Khalai Protoss from Aiur to the Dark Templar world of Shakuras. After the Zerg follow them to Shakuras, Zeratul and Artanis harness the energy of a resident Xel'Naga temple, scouring the planet of all the Zerg. The Protoss attempt to rebuild their lives on Shakuras, but are interrupted by a Zerg raid commanded by Sarah Kerrigan that kidnaps the dark templar leader Raszagal. Using Raszagal as leverage, Kerrigan coerces Zeratul into killing a new Overmind in incubation. Zeratul complies, but later kills Raszagal after it is revealed she has been brainwashed by the Zerg. Zeratul disappears while Artanis takes leadership and tries to reconstruct his people's civilization.[24]

StarCraft II: Wings of Liberty introduces the fanatical Tal'Darim, who are at odds with Jim Raynor while he attempts to find Xel'Naga artifacts for the Moebius Foundation. More significantly, Zeratul discovers that some force has successfully combined Protoss and Zerg genetic material, creating a race of incredibly powerful hybrids. Zeratul travels to Aiur to probe the corpse of the Zerg Overmind for information on an apocalyptic prophecy, and unexpectedly finds Tassadar in an ethereal form. Memories found in the Overmind's cortex depict a vision of a future in which Kerrigan is killed, whereupon the hybrids (led by an entity known only as the Dark Voice) take control of the Swarm, destroy all other forms of life, then obliterate the Zerg as well. The Protoss are the last society left standing against the Dark Voice's armies. Zeratul finds Raynor, knowing his intent to track down and defeat the Queen of Blades, and tells him to spare her life.

They also have minor appearances in StarCraft II: Heart of the Swarm, shown as antagonists to Kerrigan.

Zeratul is the early protagonist until his death at the hands of Artanis, who later became a player character in StarCraft II: Legacy of the Void. Zeratul reveals what the prophecies further after giving his memory onto Raynor. He was shocked upon learning the worst truth, an ancient race tries to destroy all life in the Universe and recreate it to his will. He tried to warn Artanis, leader of the Protoss, but was set aside when the Protoss launches an attack on Aiur to reclaim it. But the invasion is a trap set by the ancient one who corrupts the protoss, save for anyone who has no connection to Khala. Zeratul was killed trying to save Artanis by severing his nerve cords. Wracked with guilt, Artanis regrouped all survivors and set off to find survivors. Shakuras was overran by Zerg and Hybrid and the surviving Dark Templar Protoss, chose to destroy Shakuras by overloading the temple. They also ended Hybrid production by destroying the facilities, along with the Terrans that served Amon, the Ancient Xel'Naga. They also find an ancient and sealed race named Purifiers and the former Xel'Naga's minions, the Tal'Darim sided with him, with the condition that he help a rogue Ascendant to kill the leader in a duel to the death. They later reclaim Aiur again, this time successfully liberating the corrupted Protoss. Kerrigan and Raynor appears later, when another Xel'Naga calls them to the Void, Kerrigan absorbed the Xel'Naga's powers and used it to kill Amon once and for all.

The Terrans are a fictional future version of humanity in the StarCraft series. The Terrans are the most splintered of the StarCraft species, consisting of multiple factions that not only fight the other races but each other as well. Considered an adaptive and mobile species, the Terrans are noted in the lore of the series for their ability to quickly access and drain a planet's resources. The Terrans have been dedicated a full campaign in each real-time strategy video game installment to date, and are defined in-game by their specialization of units and tactics of defense and mobility. In the series' storyline, the Terrans are usually displayed as being caught in-between the conflict between the Protoss and Zerg while also dealing with frequent civil wars.

The Terrans are shown to be the most fragmented of the races in StarCraft, with multiple factions all vying for dominance over each other. Numerous factions are used throughout the series, ranging from national governments and corporations to rebels and criminals, although only four factions exhibit any major influence on the overall story arc. The first faction referred to in the backstory of the series is the United Earth Directorate (UED). A unified government of almost all the nations of Earth and several colonies both within and outside the solar system, the UED claims to operate under a policy of "enlightened socialism" but is noted for its harsh methods of public order and media censorship.[25] It is also seen as an advocate for eugenics, resulting in the mass murder of millions and exile of other unwanted criminals and genetic mutants for colonization of the distant Koprulu Sector of the galaxy in which the series takes place. The UED remains outside the events of the series until Brood War, where it takes interest in the discovery of the Protoss and Zerg, the first contact between humanity and aliens. The player controls the UED faction in Episode V of Brood War.[26]

The exiled prisoners from Earth form the Confederacy of Man in the Koprulu Sector. A de factooligarchy,[27] the Confederacy's inner workings are elaborated on in the novels Liberty's Crusade, Speed of Darkness and Nova. Taking the role of the primary antagonistic faction in StarCraft's Episode I, the Confederacy is shown as the most powerful faction in the sector at the beginning of StarCraft; in the novels, it is depicted as being brutal towards the public and corrupt at the highest levels on its capital Tarsonis.[28] The player gets to control a division of the Confederate Security Forces in the prequel shareware campaign for StarCraft. Due to the brutality of the regime, it is opposed by a variety of rebel groups and is eventually overthrown by the Sons of Korhal. The Sons of Korhal, a rebel group led by Arcturus Mengsk that the player controls during Episode I of StarCraft, form the Terran Dominion to replace the destroyed Confederacy, with the planet Korhal IV as the capital. The Dominion is an autocracy with Mengsk as its emperor.[29] The Dominion's operations are built on in The Dark Templar Saga series of novels. Although Mengsk sees himself as a benevolent dictator, he is shown to be just as harsh as his predecessors.[30]

Mengsk's actions during his campaign against the Confederacy make an enemy of Jim Raynor, one of the Sons of Korhal commanders. After Mengsk betrays other members of his command staff and reveals his real objectives of obtaining ultimate power, Raynor deserts and forms a resistance movement to the Dominion, labeled Raynor's Raiders. Described in the novels as a small army primarily consisting of members from Raynor's former colonial militia, the Raiders use the hijacked former flagship of the Sons of Korhal, the Hyperion, as their base of operations. In Queen of Blades, the group is described as being amongst the most wanted fugitives and rebels of the Dominion. The player assumes the role of Raynor in leading the group in StarCraft II Wings of Liberty.[31]

The Terrans are displayed as standard humans, and are often seen in-game in powered combat suits and with other war machines such as futuristic tanks and space battlecruisers in use by their militaries. Some Terrans are displayed with cybernetic implants.[32] Human behavior in the fictional history presented in StarCraft's manual also points to the Terrans having the ability to access and deplete a planet's natural resources at an "alarming" rate.[18] The Terrans are also noted in the backstory of the series as having a developing psionic potential. This psionic potential is what entices the Zerg to attack the Terrans, in hope of incorporating these traits into the Zerg gene pool.[33] This psionic element is shown in Terran military technology through Assassins known as Ghosts. Established as one of the iconic parts of StarCraft, Ghosts are Terrans who are born with ranging psionic abilities—from simple telepathy to advanced powers such as telekinesis or a special ability shown by Nova, where she can kill an entire skyscraper of people in a single thought known as a mind blast. These agents are cultivated by the military after being abducted from their former lives and put through an espionage training regime that can cost them their lives. In-game, the Ghost unit is equipped with a cloaking device and is designed for scouting and designating targets for nuclear strike,[34] and has been developed further through the lore of the series to the extent that the StarCraft: Ghost sub-series was once planned, specifically focusing on the life of a Ghost, Nova.

In-game, Terrans tend to favor traditional modes of warfare, often utilizing combined arms tactics with tanks, aircraft or other combat vehicles in combination with regular infantry. Using light ballistics, large calibre weapons and even tactical nuclear warheads, many Terran units are reminiscent of present-day designs. Terrans are the only race without a melee combat unit. Terrans are more adaptive than the other two races and are able to produce units at an average expense. Primary base structures can even lift off and fly to other locations, allowing players to move buildings for quicker troop deployments, access to new resource locations or to save the structures from destruction by the enemy. Terran buildings and mechanized units can be repaired if damaged, and combat medics can heal wounded organic units.[35]

The player is first fully introduced to the Terrans in Episode I of StarCraft. For a number of years before the game begins, the Confederacy is shown to be fighting a slowly losing war against the Sons of Korhal. When the Zerg and Protoss make their existence known, the pace of the war quickly changes. The player, accompanied by Jim Raynor, joins up with Arcturus Mengsk and the Sons of Korhal, and helps bring about the fall of the Confederacy by using Confederate technology to lure the Zerg into destroying the Confederate capital Tarsonis. In the process however, Mengsk abandons his second-in-command, Sarah Kerrigan, to the Zerg on Tarsonis. As a result of the brutal tactics used by Mengsk and his needless sacrifice of Kerrigan to the Zerg, Raynor abandons Mengsk and his newly formed Dominion to search for the lost Kerrigan. When Raynor finally finds her on the planet Char it is revealed that she had been captured and infested by the Zerg Overmind. He then meets Zeratul and Tassadar and consequently becomes an ally to the Protoss. Raynor's forces assist the Protoss in defending their homeworld from the Zerg and in destroying the Zerg Overmind in the game's conclusion.[23]

In Brood War's Episode V, the player takes the role of a captain in a UED expeditionary force, sent to pacify the wartorn sector after news of the discovery of the Zerg and Protoss makes its way to Earth. The UED force meets success in its initial battles, quickly bringing the Dominion to its knees and taking captive a new Overmind growing to replace the one killed by Tassadar. However, the UED fails to capture Mengsk, who allies with Raynor, Kerrigan and the Protoss templar Fenix. The UED is slowly beaten back by this mutual alliance, and although Kerrigan betrays her new allies, her Zerg forces eventually annihilate the UED fleet. Regrouping his surviving forces, Mengsk begins to reconstruct his empire, although he is still opposed by Raynor and his troops.[24]

Raynor is the protagonist and player character of StarCraft II: Wings of Liberty. Over the course of the campaign Raynor's Raiders (as his army is known) fight the Zerg and Mengsk's empire simultaneously. At the behest of a group known as the Moebius Foundation, the Raiders gather the pieces of a Xel'Naga artifact, until it is revealed that the foundation is actually led by Valerian Mengsk, Arcturus's son. Valerian intends to use the artifact's power to destroy the Queen of Blades, proving to the empire's citizens that he will be a worthy successor to the throne. Raynor begrudgingly finishes assembling the artifact and joins the imperial army in an assault on the Zerg homeworld of Char, but not before uncovering proof of Mengsk's treachery on Tarsonis and broadcasting it across the sector. The Terran forces on Char use the artifact to partially restore Kerrigan's humanity, significantly weakening her, but Raynor refuses to kill her.

The Zerg Swarm is a race of xenomorphic "hyper-evolutionary" superorganisms; they are the overriding antagonists of the StarCraft series. Unlike the Protoss and the Terrans, the Zerg are not "tool-makers", lacking technological inclination; instead, they "force-evolve" genetic traits by directed mutation in order to match such technology. Operating as a hive mind-linked 'chain of command', the Zerg strive for genetic perfection by assimilating the unique genetic adaptations of "worthy" races into their own, creating numerous different strains of Zerg. Despite being notoriously cunning and ruthlessly efficient, the majority of Zerg species have low intelligence; becoming mindless beasts if not connected to a "hive-cluster" or a "command entity".

As with the other two primary races, the Zerg are the subject of a full campaign in each of the series' real-time strategy video games. Zerg units are designed to be cheap and fast to produce, encouraging players to overwhelm their opponents with sheer numerical advantage. Since the release of StarCraft the Zerg have become a video gaming icon, described by PC Gamer UK as "the best race in strategy history".[36] The term "Zerg Rush" or "zerging" has entered video gaming lexicon to describe sacrificing economic development in favour of using many low-cost fast/weak units to rush and overwhelm an enemy by attrition or sheer numbers.[37] The tactic is infamous, with most experienced real-time strategy players being familiar with the tactic in one form or another.

The Zerg are a collective consciousness of a variety of different races assimilated into the Zerg genome. The Zerg were originally commanded by the Zerg Overmind, a manifestation of this hive mind, and under the Overmind's control the Zerg strove for genetic perfection by assimilating the favorable traits of other species.[38] After a species has been assimilated into the Swarm, it is mutated towards a different function within its hierarchy, from being a hive worker to a warrior strain. StarCraft's manual notes that some species bear little resemblance to their original forms after just a short time into assimilation (An example would be the formerly peaceful Slothien species, which was assimilated and mutated into the vicious Hydralisk strain and so on).[39] The Overmind controls the Swarm through secondary agents called cerebrates. Cerebrates command an individual brood of Zerg, each with a distinct tactical role within the hierarchy. Cerebrates further delegate power through the use of overlords for battlefield direction and queens for hive watch.[38]

The quest for 'genetic perfection' is a pseudo-religious concept to Zerg that drives them on a steady state of evolution and conflict; the zerg believed there was a state that the zerg could reach where they no longer needed to evolve, that their evolutionary form would never have to change again because they could already adapt to any situation. Abathur, an evolution master, doubted that this was possible, but reasoned that "chasing the illusion of perfection" was, regardless, tactically sound.

The vast majority of the Zerg do not have any free will as they are genetically forced to obey the commands of those further up the Zerg hierarchy, although they are sufficiently intelligent to form strategies and work as a team on the battlefield. Despite this, the average Zerg has no sense of self preservation.[40] Along with the Overmind, the cerebrates are the only Zerg with full sapience, each with its own personality and methods, although they too are genetically incapable of disobeying the Overmind.[38] The Overmind also possesses the ability to reincarnate its cerebrates should their bodies be killed, although Protoss dark templar energies are capable of disrupting this process. If a cerebrate is completely dead and cannot be reincarnated, the Overmind loses control of the cerebrate's brood, causing it to mindlessly rampage and attack anything. As a result of the Overmind's death in StarCraft and the subsequent destruction of a new Overmind in Brood War, the remaining cerebrates perished, as they could not survive without an Overmind. Sarah Kerrigan replaced the cerebrates with "brood mothers". These creatures fulfil much the same purpose, but are loyal to Kerrigan and could survive her temporary departure during the events of Starcraft 2.[citation needed]

An exception to all of this would be the Primal Zerg, who inhabit the original Zerg homeworld of Zerus (as seen in Heart of the Swarm). The Zerg Hive Mind was created to control the Zerg, and eventually put them under the control of the main antagonist of the series, the fallen Xel'Naga Amon. Some Zerg, however, managed to avoid being subsumed. These are the Primal Zerg, who have much the same genetic abilities but are not bound to the Overmind. These creatures are each independently sapient, and if they follow a leader it is because they choose to. Their lack of a Hive Mind also shields them from specific psionic attacks engineered to counter the Zerg Hive Mind.

The Zerg were created from the native lifeforms of Zerus, who had the natural ability to absorb the "essence" of creatures they killed, transforming their bodies to gain new adaptations. The Xel'Naga created the Overmind and bound the primal Zerg to its will. They gave the Overmind a powerful desire to travel across the stars and absorb useful lifeforms into the Swarm, particularly the Protoss, their previous creation, so as to become the ultimate lifeform.

The Zerg are a completely organic race, making no use of lifeless technology and instead using specialized organisms for every function. Their buildings are living creatures, as are the Leviathans that carry them across space. Zerg colonies produce a carpet of bio-matter referred to as the "creep", which essentially provides nourishment for Zerg structures and creatures.[41] The visual aesthetic of the Zerg greatly resembles that of invertebrates such as crustaceans and insects (and certainly draws inspiration from the creatures from the Alien movies). The Zerg are shown to be highly dependent on their command structure: if a Zerg should lose its connection to the hive mind, it may turn passive and incapable of action, or become completely uncontrollable and attack allies and enemies alike.

Zerg buildings and units are entirely organic in-game, and all Zerg can regenerate slowly without assistance (though not as quickly as Protoss shields). Zerg production is far more centralized than with the Terrans and Protoss; a central hatchery must be utilized to create new Zerg, with other structures providing the necessary technology tree assets, whereas the other two races can produce units from several structures. Zerg units tend to be weaker than those of the other two races, but are also cheaper, allowing for rush tactics to be used. Some Zerg units are capable of infesting enemies with various parasites that range from being able to see what an enemy unit sees to spawning Zerg inside an enemy unit. In addition, Zerg can infest some Terran buildings, allowing for the production of special infested Terran units.[42]

In StarCraft, the Zerg are obsessed with the pursuit of genetic purity, and are the focus of the game's second episode. With the Xel'Naga–empowered Protoss targeted as the ultimate lifeform, the Zerg invade the Terran colonies in the Koprulu Sector to assimilate the Terrans' psionic potential and give the Zerg an edge over the Protoss. Through the actions of the Sons of Korhal, the Zerg are lured to the Confederate capital Tarsonis, where they capture the psionic ghost agent Sarah Kerrigan and infest her. Returning to the Zerg base of operations on Char, the Zerg are attacked by the dark templar Zeratul, who accidentally gives the location of the Protoss homeworld Aiur to the Zerg Overmind. With victory in sight, the Overmind launches an invasion of Aiur and manifests itself on the planet. However, at the end of the game, the Protoss high templar Tassadar sacrifices himself to destroy the Overmind, leaving the Zerg to run rampant and leaderless across the planet.[23]

The Zerg return in Brood War initially as uncontrolled indiscriminate killers without the will of the Overmind to guide them. Through the early portions of Brood War, Sarah Kerrigan is at odds with the surviving cerebrates, who have formed a new Overmind to restore control of the Swarm. Through allying herself with the Protoss, Kerrigan strikes at the cerebrates, causing disruption of their plans. Eventually, the UED fleet takes control of Char and pacifies the new Overmind with drugs, putting the cerebrates and most of the Zerg under their control. Kerrigan retaliates by forming a tenuous alliance with the remnants of the Dominion and the forces of Jim Raynor and Fenix, their subsequent victories turning the tide against the UED. However, she later betrays the alliance by dealing long-term damage to the infrastructures of her allies and killing Fenix. Proceeding to blackmail Zeratul into killing the new Overmind, Kerrigan's forces destroy the remnants of the UED fleet, giving her full control of the Zerg and establishing the Swarm as the most powerful faction in the sector.[24]

In StarCraft II: Wings of Liberty, Jim Raynor and the rebel forces who oppose both the Dominion and the Zerg, manage to secure an ancient Xel'Naga artifact and after successfully infiltrating Char, they use it to subjugate the Zerg and restore Kerrigan's human form. Once again without a unified leadership, the Zerg get divided into multiple broods feuding over control of the Swarm. This situation persists until the events of StarCraft II: Heart of the Swarm. Kerrigan, believing Raynor to have been killed in a Dominion surprise attack, enters the original Zerg spawning pool to become the Queen of Blades again. This time she is no longer motivated to destroy humanity, having kept more of her original mindset due to the non-interference of the Zerg Hive Mind, and by extension, the Dark Voice, Amon.

Kerrigan is the protagonist and player character of StarCraft II: Heart of the Swarm. After being deinfested, she was taken in Valerian Mengsk's hideout to research on her, until the Dominion attacks the facility, she escaped along with the rest of the facility, except Raynor, who was captured by Nova. She later learned that Raynor was executed and seeks revenge on Arcturus. As she enters a Leviathan, she controls the local Swarm inside, and starts rebuilding her forces from scratch. She later evolved into a Primal Zerg after a confrontation with Zeratul, leading her to the origins of the Zerg. She became a Primal, after absorbing the spawning pool and killing Primal Leaders to collect essence. With her newfound power, she initially takes the fight to the Dominion after subduing countless Queens. She was later shocked after she knows that Raynor survived and held by Dominion as a bargaining chip. She organizes a raid, rescuing Raynor but the man fell into disbelief that the one he saved, returns to being a monster. She also confronted an ancient Shapeshifter creating Hybrids at the behest of her former rival named Alexei Stukov. She later prepared to end Arcturus Mengsk's reign by killing him in his palace in Korhal. She later left to confront the Shapeshifter's master.

The Xel'Naga (whose name, according to the original StarCraft manual, means "Wanderers from Afar") are an ancient race that has to date only been featured in the lore of the StarCraft series; their only appearances have been in the form of relics. The Xel'Naga play important roles in the backstories to both the Protoss and Zerg, being responsible for manipulating the evolution of the two races, along with an unknown number of other species. It was speculated that a player could control the Xel'Naga in StarCraft II and although this has been firmly denied by Blizzard Entertainment,[43] they have confirmed the Xel'Naga will contribute to the game's storyline "in a rather epic tale".[44]

In the manual to StarCraft, the Xel'Naga are described as a race determined to create the perfect lifeform. The Xel'Naga are also stated to have come from another galaxy and to have "seeded and cultivated thousands of various species" in their time.[45] The Xel'Naga guided the evolution of the Protoss, a species the Xel'Naga believed possessed purity of form. However, after revealing themselves to their seemingly successful experiment, their presence caused the Protoss to devolve into a fearful and tribalistic mindset. Believing their experiment a failure, the Xel'Naga were shunned and eventually attacked by the Protoss while departing Aiur.[46]

The Xel'Naga then discovered the Zerg, small parasitic larvae that could control the nervous systems of other species. The Xel'Naga saw this as purity of essence, and guided the evolution of the Zerg as well. However, the Zerg were animals, concerned only with self-preservation. To help further the Zerg as a species, the Xel'Naga created the Overmind, a central consciousness to organize the Zerg. They hid their existence from the Overmind, however. On becoming aware of their existence (after being filled with an overriding directive it could not fight off), the Overmind attacked the Xel'Naga, infesting and destroying the greater whole of the race. In StarCraft II Wings of Liberty, Xel'Naga watchtowers provide vision in a large circular radius around the tower.[47]

Although the Xel'Naga rarely appear during the novels and the video games, various relics left behind from their legacy are scattered throughout the series. One such relic appears in Brood War, a large temple on the planet Shakuras containing the power to wipe the planet clear of other species.[48] During the course of Brood War, the Protoss activate the temple and use it to destroy all of the Zerg on Shakuras.[49] In addition, other structures have been shown in the series. In the novel Shadow of the Xel'Naga, the three main species fight for control of a large Xel'Naga artifact on the planet Bhekar Ro, but accidentally activate it. The artifact releases a creature incubating in the structure, which proceeds to convert the nearby Xel'Naga-empowered Protoss and Zerg forces into energy for nourishment, before disappearing into space.[50] After this, the novel Firstborn reveals that numerous other similar artifacts are discovered by the Terran Dominion within its borders. The Dominion heir Valerian Mengsk consequently sends an archaeological team under Emil Narud to investigate these relics.[51]StarCraft II: Wings of Liberty also features a Xel'Naga relic that was broken into pieces. James Raynor and Valerian Mengsk reunite the pieces and, during a bloody invasion of the volcanic Zerg planet of Char, use the relic to restore Sarah Kerrigan back into her human form;[52] the artifact also plays a significant role in Starcraft II: Legacy of the Void.

The species of StarCraft have been popular enough to inspire the creation of several collectable statues and toys based on in-game units. The first series of action figures was released by ToyCom in 2003 and included the Terran heavy infantry firebat[53] with markings similar to some original StarCraft concept art for the firebat[54] and a hydralisk, the Zerg medium assault warrior strain.[55] A series of toys were also made available in 1998,[56] featuring two colour variations of the Terran marine, another hydralisk and a Protoss zealot, the basic Protoss infantry ground unit. In addition, 1/30 scale model kits for the marine and hydralisk were released in 1999 by Academy Hobby Model Kits.[57] A second series of collectable statues, which included one based on the Terran ghost, a Terran espionage agent with psychic powers, was in development but appears to have been cancelled.[58]

Before StarCraft, most real-time strategy games consisted of factions and races with the same basic play styles and units with mostly superficial differences. Thus, the uniqueness and variety of the species in the StarCraft series has been well received by many of the industry's critics. In their review for StarCraft, IGN's Tom Chick stated that the balance and difference between the races was "remarkable", continuing to praise the game's "radical" approach to different races and its high degree of success when compared with other games in the genre. IGN was also positive about the unit arrangements for the three races, crediting Blizzard Entertainment for not letting units become obsolete during extended play and for showing an "extraordinary amount of patience in balancing them."[6]GameSpot was complimentary of the species in its review for StarCraft, describing the races as being full of personality. Stating that the use of distinct races allowed for the game "to avoid the problem [of equal sides] that has plagued every other game in the genre", GameSpot praised Blizzard Entertainment for keeping it "well balanced despite the great diversity."[7]

Other reviews have echoed much of this positive reception. The site The Gamers' Temple described the species as "very diverse but well-balanced, " stating that this allowed for "a challenging and fun gaming experience."[59]Allgame stated that the inclusion of three "dynamic" species "raises the bar" for real-time strategy games, complimenting the game for forcing the player to "learn how [the aliens'] minds work and not think like a human".[60] Commentators have also praised the aesthetic design of the three races; in particular, the powered armor worn by the Terran Marine was rated eleventh on in a Maxim feature on the top armor suits in video games,[61] and ninth in a similar feature by Machinima.com.[62]

This positive view, however, is not universally held. For example, Computer and Video Games, while describing the game as "highly playable, " nevertheless described a "slight feeling of déjà vu" between the three races.[63]